1. Field of the Invention
This invention is in the fields of air fuel mixture stratifiers and igniters for internal combustion engines of the piston and cylinder type, wherein a jet of air fuel mixture can be used to create a stratified principal air fuel mixture in the combustion chamber of the engine cylinder.
2. Description of the Prior Art
The Hesselman engine combustion process, and the more recent Texaco combustion process, are examples of early prior art air fuel mixture stratifiers, which created a stratified principal air fuel mixture in the engine combustion chamber. Descriptions of examples of these prior art mixture stratifier schemes are presented in the following references:
(i) "A High Power Spark-Ignition Fuel Injection Engine," Trans. SAE, Vol. 35, p. 431, 1934; PA1 (ii) "The Elimination of Combustion Knock-Texaco Combustion Process," SAE Quarterly Trans., Vol. 5, p. 26, 1951; PA1 (iii) "The Elimination of Combustion Knock," E. Barber, J. Malin, J. Mikita, Jour. of the Franklin Institute, Vol. 241, p. 275, April 1946;
In these prior art Texaco combustion processes, a jet of liquid fuel was injected into the engine combustion chamber, near the end of the compression stroke. The air inside the engine cylinder was set into rotary motion during intake, by use of shrouded intake valves, or specially oriented intake ports and manifolds. The liquid fuel spray was carried by the rotating air into which it was injected, toward a spark igniter. When this stratified air fuel mixture reached the spark, evaporated portions of the fuel, diffused into the surrounding air, were ignited by the spark, and a burning zone was thus created. The heat generated in this burning zone, evaporated those fuel portions unevaporated at the time of spark ignition and subsequent interdiffusion of air and thusly evaporated fuel maintained the burning zone, until most of the injected liquid fuel was burned. This burning process somewhat resembles that of a conventional liquid fueled oil burner, except that it is carried out intermittently and at high pressure.
Since air fuel vapor mixture is burned very shortly after being created, time is not available for expiration of the compression ignition delay period, which leads to engine knock. Thus one principal advantage of the Texaco combustion process was that high engine compression ratio, and hence high engine efficiency, could be achieved while using fuels of low octane number, and hence low knock resistance. Such low octane number fuels are generally of lower cost than high octane number fuels.
Engine torque was adjusted, for this Texaco combustion process, by proportionally adjusting the liquid fuel quantity injected into the engine cylinder, using fuel injection pumps and nozzles very similar to diesel engine injection pumps and nozzles. Since a stratified mixture was used, the air quantity inside the engine cylinder did not require adjustment, and an intake manifold throttle valve was not used. In consequence, the engine efficiency losses due to intake air throttling were avoided. Hence another principal advantage of the Texaco combustion process, was that high engine efficiency could be obtained at low engine torque since the usual throttling and consequent pumping power loss was avoided.
Liquid fuel, unevaporated at the start of burning, becomes surrounded by very hot burned gases, essentially devoid of oxygen. Rapid evaporation of liquid followed, but in the absence of oxygen, this evaporated fuel produced a high yield of soot particles, in a manner similar to soot production in diesel engines. Appreciable portions of this soot survives to exhaust to create an undesirable exhaust soot emission.
The injected liquid fuel volume, being much smaller than the air volume needed for burning, it is difficult to distribute the liquid spray particles uniformly throughout the cylinder air mass. In consequence the available cylinder air mass is incompletely utilized for burning. For this reason a larger engine displacement is needed, resulting in increased engine weight and cost than for a comparable conventional gasoline engine.
The liquid fuel is injected at high pressure, and the fuel injector must withstand subsequent peak combustion pressures and high heat transfer rates which follow. The fuel injection equipment is thus essentially similar to that used with conventional diesel engines and is expensive.
These then are the principal disadvantages of the Texaco combustion process; that exhaust soot is emitted, that a larger engine displacement is needed, and that expensive fuel injection equipment is required. It would be desirable to have available an engine system capable of realizing the knock suppression and reduced pumping friction loss characteristics of this Texaco combustion system, but possessing reduced soot emissions, better air utilization, and lower cost fuel injection apparatus.